In my case, I could not figure this either to the point that I thought I have drivetrain/diff noise. I looked at the procedure to change the hub and it wasn't bad, so bought one from AZ, put it in the passenger side (felt to be more noisy), noise was a bit better. Then chnaged the driver side and all was well. So in my case both were bad, I guess that is what we call consitent quality in manufacturing.